Automatic mode selection in a controller for grading implements

ABSTRACT

A method is disclosed for a controller to automatically switch to an alternative control mode to control the height of a grading implement when the output of a positioning sensor is not available. According to the invention, the controller recognizes sensor unavailability and automatically switches to an alternative operating mode to maintain control. In one alternative operating mode, the controller recognizes sensor unavailability and automatically routes the control signal from the unaffected side to the control channel for the affected side. In another alternative operating mode, the controller monitors the current value of an additional sensor for an alternative mode of control until one of the primary sensors becomes unavailable, and then automatically switches to the alternative mode for the affected side, using the last known value for the alternative mode as the set point.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to machine control systems thatcontrol the orientation of a grading implement on a constructionmachine. Specifically, the invention is a method to automate theselection of various alternative operating modes of the controller toeliminate the need for manual operator intervention when a positioningsensor is inoperative.

[0003] 2. Description of the Relevant Art

[0004] Current control systems used for controlling grading implementsfor earth moving and the like may have several automatic operating modesusing different positioning sensors or control methods. In this case, anoperator needs to select a single operating mode. This selection is donemanually by the operator who determines when and what mode to select forautomatic control. If the operator selects a mode that does not have afunctioning sensor currently connected to the system or if a selectedsensor is currently not providing data for control, the control systemwill switch from automatic mode to manual mode. When this happens, theoperator must either manually switch the system to another automaticmode (which uses an active sensor) or somehow provide inputs to thecontroller that mimic the inactive sensor.

[0005] For example, if the machine is set up to control height relativeto a rotating laser reference plane, each end of the grading implementwould have a laser receiver extending vertically on a mast. FIG. 1 showsa laser-controlled concrete screed as an example of such a system. Thescreed 10 is a grading implement that is moved by a boom 12 that extendsoutwardly from a base 16. Two masts 14 have laser receivers that sense arotating laser used as a height reference. The laser receivers areconnected to a control system that outputs control signals to hydraulicvalves at each end of the screed. The receivers sense the verticalposition of the laser beam and the control system uses this sensedposition to control the elevation of the grading implement with respectto the laser reference plane.

[0006] If during movement of the machine a laser receiver moves to aposition where the beam from the laser is blocked, the normal responseof the control system is to turn off the control outputs for theaffected side. The laser receiver on the opposite side may have anunobstructed path to the laser and, if so, continues to operate in anormal manner. This may happen, for example, when the concrete screed isused inside a building and interior posts block the laser beam atcertain positions.

[0007] The effect of these periods of sensor blackout or unavailabilityon the final elevation of the grade depends on the movement of theimplement during the blackout periods and the desired tolerance of thefinished grade. If the uncontrolled movement of the implement during theblackout periods would result in a surface that exceeds the requiredfinish tolerance, the operator must intervene to mitigate the problem.Aside from the present invention, there are two methods of operatorintervention in this circumstance—open loop and closed loop.

[0008] In an open-loop intervention, the operator must provide controlsignals to the controller for the affected side by using the manualcontrols for that side. The operator may accomplish this by manuallycontrolling the elevation of the affected side by visually matching aprevious pass. Or, the operator may attempt to manually input the samecontrol signals as the unaffected side. This intervention is practicalonly if the control signals are simple on/off signals and arerepresented on a control display by lights or other easily identifiableindicators.

[0009] In a closed-loop intervention, the operator must change thecurrent mode of the control system from laser mode to an alternativecontrol mode that uses a different sensor, such as a sonic elevationsensor or a slope sensor. The operator accomplishes this in a typicalcontrol system by putting the system in manual, switching the system tothe alternative control mode, entering the current elevation or slope toinitialize the new mode, and then re-enabling the system for automaticcontrol. The operator must make these multiple inputs quickly or theimplement may move outside of the required tolerance during thetransition period.

[0010] The final grading finish depends on prompt operator action andtherefore may degrade if the operator is distracted or otherwise unableto intervene during a blackout period.

SUMMARY OF THE INVENTION

[0011] In summary, the present invention is a method for automaticallyswitching to an alternative control mode when the output of apositioning sensor is not available. The present invention replacesmanual intervention by the operator with a new automatic method ofintervention by the controller. According to the invention, the controlsystem recognizes the periods of sensor blackout or unavailability andautomatically switches to an alternative operating mode to maintaincontrol. The control system can make this decision based upon apredetermined priority for the available sensors and control modes andcan switch back to the most preferable mode available when the sensorsare available and operating.

[0012] The present invention has two basic modes of operating, open loopand closed loop. In the open-loop mode, the controller recognizes thesensor blackout or unavailability on the affected side and automaticallyroutes the control signal from the unaffected side to the controlchannel for the affected side. The controller continues this mode ofoperation until the affected sensor is available and valid again andthen reinstates the original mode of operation. Since the controller isrerouting the control signals, the signals can be more complex thansimple on/off signals that manual intervention could handle. Theresulting finish will be closer to the desired tolerance and thecorrective movement of the implement will be less when the unavailablesensor signal is reacquired.

[0013] In the closed-loop mode, the controller of the invention monitorsthe current value of an additional sensor for an alternative mode ofcontrol until one of the primary sensors loses its signal. Thecontroller then automatically switches the mode for the affected side tothe alternative mode, using the last known value for the alternativemode as the set point. The controller remains in this alternative modeuntil recovery from the blackout (sensor unavailability) and thenswitches back to the original mode.

[0014] The features and advantages described in the specification arenot all inclusive, and particularly, many additional features andadvantages will be apparent to one of ordinary skill in the art in viewof the drawings, specification and claims hereof. Moreover, it should benoted that the language used in the specification has been principallyselected for readability and instructional purposes, and may not havebeen selected to delineate or circumscribe the inventive subject matter,resort to the claims being necessary to determine such inventive subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of a prior Somero S-160 laser screed,which is one possible platform for the present invention.

[0016]FIG. 2 is a diagram of an open-loop mode of operation of thepresent invention under normal operating conditions.

[0017]FIG. 3 is a diagram of the open-loop mode of operation of thepresent invention under a sensor-blackout condition.

[0018]FIG. 4 is a diagram of a closed-loop mode of operation of thepresent invention under normal operating conditions.

[0019]FIG. 5 is a diagram of the closed-loop mode of operation of thepresent invention under a sensor-blackout condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The drawings depict various preferred embodiments of the presentinvention for purposes of illustration only. One skilled in the art willreadily recognize from the following discussion that alternativeembodiments of the structures and methods illustrated herein may beemployed without departing from the principles of the inventiondescribed herein. The description omits basic information about gradingimplement control systems, which a person of ordinary skill is presumedto know.

[0021] The present invention is a method for automatically switching toan alternative control mode when the output of a positioning sensor isnot available and switching back to a preferred control mode when thesensor becomes available again. According to the invention, the controlsystem recognizes periods of sensor unavailability, and thenautomatically switches to an alternative operating mode to maintainautomatic control. The control system can make this decision based upona predetermined priority for the available sensors and can switch backto the most preferable mode available when the associated sensors areavailable and operating. The present invention reduces the need forintervention by the operator to produce acceptable grading results.

[0022] The present invention has two basic modes of operation, open loopand closed loop, as explained below.

[0023] Open Loop

[0024] In the open-loop mode, the controller of the invention recognizesthe sensor blackout or unavailability on the affected side andautomatically routes the control signal from the unaffected sensor tothe affected side. The controller continues this mode of operation untilthe affected sensor is available again. When the controller recognizesthat both sensors are active, it reinstates the original mode ofoperation. Since the controller is outputting the control signals, thesignals can be more complex than the simple on/off controls required formanual open-loop intervention according to prior practice. For example,the control signals compatible with the invention may be proportionalcontrol signals instead of simple on/off signals. The resulting gradingfinish will be closer to the desired tolerance and the correctivemovement of the grading implement will be less when the unavailablesensor signal is reacquired.

[0025]FIGS. 2 and 3 illustrate the open-loop mode of the invention withtwo sensors 20 and 22. The sensors 20 and 22 may be laser receivers asdescribed above, although other sensors, such as sonic distance sensorsor contacting sensors or other position-sensing devices, could be used.FIG. 2 shows the system in normal operation when both sensors 20 and 22generate output signals 24 and 26 that are input to a controller 28. Thecontroller 28 outputs left and right control signals 30 and 32 thatcause hydraulic cylinders 34 and 36 (or other motive devices) to raiseor lower the grading implement.

[0026] In normal operating mode, the controller 28 controls the heightof the left side of the implement according to the output of the leftsensor 20. The left sensor 20 supplies its output signal 24 to thecontroller 28, which generates the control signal 30 and supplies it tothe left-side hydraulic cylinder 34 to cause the left side of thegrading implement to be raised or lowered to reduce any deviation from adesired set point.

[0027] Similarly, the controller 28 controls the height of the rightside of the implement according to the output of the right sensor 22 innormal operating mode. The right side sensor 22 supplies its outputsignal 26 to the controller 28, which generates the control signal 32and supplies it to the right-side hydraulic cylinder 36 to cause theright side of the grading implement to be raised or lowered to reduceany deviation from the set point.

[0028] Arrows 38 and 40 indicate that this is a closed-loop controllerfor each side of the grading implement. The hydraulic cylinders 34 and36 respond to the controller by moving the implement up or down. The upand down movement of the implement is detected by the sensors 20 and 22and fed back to the controller 28.

[0029]FIG. 3 illustrates the method of the present invention when theright sensor 22 is blocked or otherwise unavailable and does not outputa valid signal. The sensors 20 and 22 and the controller 28 are inconstant communication because the controller periodically samples thestatus and output of the sensors. In the preferred embodiment, eachsensor has a vertically-disposed linear array of laser detectors, withthe center being the set point. The positioning error is determined bywhich detector in the linear array detects the laser and how far it isfrom the center of the array. The laser beam that provides the referenceplane is a rotating laser that rotates at least five revolutions persecond. This means that the sensor expects to detect the laser every 200milliseconds. If more than 200 milliseconds elapses, then the sensorassumes that the laser light is blocked and signals the controller 28accordingly. This is accomplished by a 250 millisecond timer, which isreset by each detected laser strike.

[0030] If the timer in the right sensor 22 times out, then the sensorsignals the controller 28 that no laser is detected. In that case, theoutput signal 24 of the left sensor 20 is used by the controller 28 tocontrol both sides of the implement. The controller 28 uses the validoutput signal 24 to generate both control signals 30 and 32. The leftside feedback path 38 is still intact, but the right side is operatingopen loop because the right sensor is temporarily inoperative.

[0031] When the right sensor 22 reacquires the laser and outputs a validsignal 26, the controller 28 switches back to the normal mode shown inFIG. 2. The controller 28 continuously monitors the status of thesensors 20 and 22, so when the right sensor 22 signals the controllerthat it has detected the laser, the controller switches to the normalmode.

[0032] If the left sensor signal 24 is unavailable or invalid but theright sensor signal 26 is available, then the controller 28 uses theright sensor signal to control the elevation of both left and rightsides of the grading implement.

[0033] Closed Loop

[0034] In the closed loop mode of the present invention, there is anadditional sensor and associated control circuitry providing analternative control mode that is used as a backup when a primary sensoris blocked or otherwise unavailable. The controller of the inventionmonitors the current value of the alternative control mode until aprimary sensor is blocked or otherwise unavailable and loses its signal.The controller then automatically switches to the alternative controlmode for the affected side, using the last known output of thealternative sensor as the set point. This maintains the position of theaffected side of the grading implement during the period in which theprimary sensor is unavailable. The controller remains in thisalternative mode until the primary sensor is available again, and thenswitches back to the original mode.

[0035] The operation of the closed-loop mode of the invention isillustrated in FIGS. 4 and 5. FIG. 4 shows the control system in normaloperation, where both primary sensors 20, 22 generate output signals 24,26 and the controller 28 and cylinders 34 and 36 control the height ofthe right side of the implement according to the right sensor andcontrols the height of the left side of the implement according to theleft sensor. The output 44 of an alternate sensor 42 is also monitoredand temporarily stored by the controller 28. The primary sensors 20 and22 may be, for example, two laser receivers and the alternate sensor 42may be a slope sensor or an ultrasonic distance sensor.

[0036]FIG. 5 illustrates what happens in the present invention when theright sensor 22 is blocked or otherwise unavailable and does not outputa valid signal. In that case, the controller 28 uses the output 44 ofthe alternate sensor 42 to control the right side of the implement. Thelast signal output by the alternate sensor 42 prior to the right sensor22 becoming unavailable is used as a set point for the right channel ofthe controller 28. The controller 28 generates a control signal 32 toraise or lower the right side of the grading implement to minimize thedeviation from that set point. In other words, the alternate sensor 42is used to keep the right side in the same position or attitude as itwas in when the primary sensor 22 became blocked. The movement of theimplement affects the alternate sensor 42, thus providing a feedbackpath 46 and closed-loop control of the implement height.

[0037] When the unavailable sensor signal 26 is reacquired, the controlsystem shifts back to its normal mode, as shown in FIG. 4. Thedescription above assumes that the right sensor is unavailable, but theclosed-loop mode of the present invention also operates when the leftsensor is unavailable.

[0038] One preferred embodiment of the present invention includes laserreceivers as the primary sensors 20 and 22, and a slope sensor as thealternate sensor 42. When one of the laser receivers is blocked, thenthe controller 28 automatically switches to a mode where the slopesensor is used to generate the control output for the affected side. Thecontroller 28 uses the last signal output by the slope sensor prior tothe blockage as the set point. The control system controls the height ofthe affected side to maintain the same slope of the implement as whenthe blockage occurred. When the blocked laser receiver becomes availableagain, operation reverts to both laser receivers and the slope sensorreverts to its backup role.

[0039] Both the open- and closed-loop modes of the present invention canbe available in the controller 28 at the same time. The controller 28selects the appropriate mode based upon a predetermined priority set bythe operator.

[0040] Furthermore, there may be more than one alternate sensor for theclosed-loop mode, and a selection priority among the alternative sensorscan be set by the operator. If the quality of the signal is available ina form other than on/off, e.g., a proportional control signal, then thecontroller 28 can select between the alternate sensors based on a userentered threshold level.

[0041] The sensors and associated control systems are not intended to belimited to just the examples presented above, unless so specified in theclaims. The primary sensors could be laser receivers as discussed above,but they also could be other sensors such as sonic distance sensors orGPS (global positioning satellite). Furthermore, the alternate sensorsused in the closed-loop mode can be sonic distance sensors, slopesensors, accelerometers or inertial platforms, laser receivers, GPS, ora variety of contact sensors.

[0042] From the above description, it will be apparent that theinvention disclosed herein provides a novel and advantageous method forgrading-implement controllers that automatically switches to analternative control mode when the output of a positioning sensor is notavailable. The foregoing discussion discloses and describes merelyexemplary methods and embodiments of the present invention. As will beunderstood by those familiar with the art, the invention may be embodiedin other specific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting, of the scopeof the invention, which is set forth in the following claims.

What is claimed is:
 1. A method for operating a controller forcontrolling the height of a grading implement, comprising the steps of:providing a left sensor that outputs a left-side output signalindicative of the height of the left side of the grading implement;providing a right sensor that outputs a right-side output signalindicative of the height of the right side of the grading implement;providing a controller that is responsive to the left-side output signalfor controlling the height of a left side of the grading implement andis responsive to the right-side output signal for controlling the heightof a right side of the grading implement; operating the controller tocontrol the height of the grading implement by responding to theleft-side and right-side output signals when both are available; and ifthe left-side or right-side output signal is unavailable, thenautomatically using an alternative sensor to control the height of thegrading implement on the side of the unavailable output signal.
 2. Amethod as recited in claim 1 wherein the step of automatically using analternative sensor includes using the right-side output signal tocontrol both sides of the grading implement if the left-side outputsignal is unavailable, and using the left-side output signal to controlboth sides of the grading implement if the right-side output signal isunavailable.
 3. A method as recited in claim 1 wherein the step ofautomatically using an alternative sensor includes using an outputsignal of a third sensor to control the side of the grading implementhaving an unavailable output signal.
 4. A method as recited in claim 3further including a step of monitoring the output signal of the thirdsensor while the left-side and right-side output signals are available,and using the last monitored value of the output signal of the thirdsensor as a set point when the left-side or right-side output signalbecomes unavailable.
 5. A method as recited in claim 3 wherein the thirdsensor is a slope sensor.
 6. A method as recited in claim 3 wherein thethird sensor is a distance sensor.
 7. A method as recited in claim 1further comprising a step of ceasing to use the alternative sensor whenthe unavailable output signal becomes available again.
 8. A method asrecited in claim 1 wherein the left and right sensors are laserreceivers.
 9. A method as recited in claim 1 wherein the gradingimplement is a concrete screed.
 10. A method for operating a controllerfor controlling the height of a grading implement, comprising the stepsof: providing a left sensor that outputs a left-side output signalindicative of the height of the left side of the grading implement;providing a right sensor that outputs a right-side output signalindicative of the height of the right side of the grading implement;providing a controller that is responsive to the left-side output signalfor controlling the height of a left side of the grading implement andis responsive to the right-side output signal for controlling the heightof a right side of the grading implement; operating the controller tocontrol the height of the grading implement by responding to theleft-side and right-side output signals when both are available; if theleft-side output signal is unavailable, then automatically using theright-side output signal to control both sides of the height of thegrading implement; and if the right-side output signal is unavailable,then automatically using the left-side output signal to control bothsides of the height of the grading implement.
 11. A method for operatinga controller for controlling the height of a grading implement,comprising the steps of: providing a left sensor that outputs aleft-side output signal indicative of the height of the left side of thegrading implement; providing a right sensor that outputs a right-sideoutput signal indicative of the height of the right side of the gradingimplement; providing a controller that is responsive to the left-sideoutput signal for controlling the height of a left side of the gradingimplement and is responsive to the right-side output signal forcontrolling the height of a right side of the grading implement;operating the controller to control the height of the grading implementby responding to the left-side and right-side output signals when bothare available; and if the left-side or right-side output signal isunavailable, then automatically using an output signal of a third sensorto control the side of the grading implement having an unavailableoutput signal.